Hosts, such as storage devices (e.g., hard disk drives and optical drives) and storage device controllers, can communicate with each other via cables. Often, these cables are serial cables which transfer a single bit per clock cycle. Unfortunately, these serial cables do not include mechanisms that can monitor and/or store diagnostic data about the signals sent to and received from the hosts and/or the cables. Thus, the cause of a communication failure or degradation is difficult to determine, i.e. whether the host (or hosts) is failing or whether the serial cable is failing. For example, in a degrading system, a serial cable that is failing may produce the same symptoms (e.g., a degraded signal) as a host that is failing. Therefore, it would be highly desirable to provide a system and method for diagnosing operation or failure of a serial communication bus or link.